Generic road building machines are known. In one known machine, the mill comprises an automotive travelling mechanism. A total of four support wheels, two at the front and two at the rear, are arranged on the automotive travelling mechanism, with embodiments with only one front support wheel being known. The front axle of the undercarriage is arranged to be steerable. Furthermore, a working device is present which is mounted in or on the machine frame and is approximately flush with the machine frame. The working device concerns a cylindrical milling drum in the case of a cold milling machine for example which is arranged in the rear region of the machine frame. Since the milling drum is arranged in the manner that it is virtually flush with a front side with the lateral edge of the machine frame, the machine is also capable of milling close to the edges since the working device can be moved directly past the edge. It is advantageous for a stable guidance of the machine however when the two rear support wheels enclose the milling drum along its rotational axis on both sides and are disposed at one level in the working direction of the mill. It is therefore also known to arrange the rear support wheel which is disposed on the null side laterally from the face side of the working device to the outside, so that it protrudes laterally beyond the machine frame. In order to enable milling that is near to an edge with one and the same mill and in order to achieve a stable guidance of the machine if milling close to the edge is not desired at the same time, the rear support wheel which is disposed on the null side can be arranged to be horizontally pivotable, so that it can be positioned, as required, in the inwardly or outwardly pivoted state.
It is known for this purpose to provide a swivel unit on the mill, comprising an articulation area formed by the machine frame and a swivel arm which carries the rear support wheel on the null side at its one end and is pivotably linked at its other end to the articulation area of the machine frame. The articulation area of the swivel unit designates the part of the machine frame in which the pivot bearing for the inwardly and outwardly pivotable swivel arm is arranged on the machine frame. This does not only relate to the direct contact area of the respective articulated connection, but rather also the portion of the machine frame adjacent to this area. The swivel unit is specifically arranged in the manner that it can be pivoted between an “outwardly pivoted position” in which the rear wheel which is on the null side is pivoted outwardly to an outer end position parallel to the longitudinal direction of the machine frame and an “inwardly pivoted position” in which the rear support wheel which is on the null side is inwardly pivoted to an inward end position which is parallel to the longitudinal direction of the machine frame. If milling close to the edge is desired or if the road building machine is to be as narrow as possible for transport purposes for example, the rear support wheel which is on the null side will thus be pivoted to the “inwardly pivoted position”. It is alternatively also possible to outwardly pivot the support wheel to its “outwardly pivoted position” and thus improve the travelling properties of the road building machine for example.
In order to enable the integration of the pivoting of the pivot wheel especially well into the operation of the machine, it is further known to provide a pivot bearing which enables the automatic displacement of the pivot unit between the “outwardly pivoted position” and the “inwardly pivoted position”. The pivoting axis usually extends vertically and the pivoting movement between the “inwardly pivoted position” and the “outwardly pivoted position” in a horizontal plane. One disadvantage of known pivot units is their continued need for much space which is principally caused by the arrangement of the gear in a horizontal plane. This causes problems to housing the pivot unit especially in compact road building machines, especially in the “inwardly pivoted position”.